Classifications

• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C8/00—Enamels; Glazes; Fusion seal compositions being frit compositions having non-frit additions
  • C03C8/02—Frit compositions, i.e. in a powdered or comminuted form
  • C03C8/06—Frit compositions, i.e. in a powdered or comminuted form containing halogen
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C8/00—Enamels; Glazes; Fusion seal compositions being frit compositions having non-frit additions
  • C03C8/14—Glass frit mixtures having non-frit additions, e.g. opacifiers, colorants, mill-additions
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C8/00—Enamels; Glazes; Fusion seal compositions being frit compositions having non-frit additions
  • C03C8/14—Glass frit mixtures having non-frit additions, e.g. opacifiers, colorants, mill-additions
  • C03C8/20—Glass frit mixtures having non-frit additions, e.g. opacifiers, colorants, mill-additions containing titanium compounds; containing zirconium compounds
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23D—ENAMELLING OF, OR APPLYING A VITREOUS LAYER TO, METALS
  • C23D5/00—Coating with enamels or vitreous layers

Definitions

• the invention relates to porcelain enamel coatings, and particularly, to water-resistant porcelain enamel coatings for use in water heaters.
• Porcelain enamel is subject to corrosion and dissolution by hot water. This can cause difficulties in applications such as hot water heaters. In a water heater, once the porcelain enamel coating protecting a metal substrate is dissolved through to the substrate, then the substrate corrodes rapidly and is perforated through. At this point the water heater must be replaced.
• the invention provides a method of manufacturing a water-resistant porcelain enamel coating.
• the method comprises providing a ground glass; adding mill additions including silica and a zirconia compound to form a mixture; applying the mixture to a substrate; and firing the coated substrate to form the porcelain enamel coating.
• the resulting coating has good water-resistance properties, good adhesion to the substrate, and minimal cracking. Therefore, this coating is useful, for example, to increase the life of water heaters.
• the invention also provides a porcelain enamel coating prepared by the above process, and a water heater coated with the porcelain enamel.
• the invention provides a method of manufacturing water-resistant porcelain enamel coating.
• the method comprises providing ground glass and adding mill additions to the ground glass to form a mixture, wherein the mill additions comprise silica and a zirconia compound.
• the mixture is applied to a metal substrate to form a coated substrate, and the coated substrate is fired to form the water-resistant porcelain enamel coating.
• the silica and zirconia compound mill additions may comprise at least about 25 and less than about 70 parts by weight per hundred parts by weight ground glass.
• the invention provides a method of manufacturing a water-resistant porcelain enamel coating suitable for use on a water heater.
• the method comprises providing a ground borosilicate glass, and adding mill additions to the ground glass to form a mixture.
• the mill additions comprise (a) a zirconia compound constituting at least about 10 parts by weight per hundred parts by weight ground glass and (b) a silica compound.
• the mixture is applied to a water heater and the water heater is fired at a temperature of about 1000° F. to about 1700° F. to form the water-resistant porcelain enamel coating.
• the invention provides a method of manufacturing a water-resistant porcelain enamel coating.
• the method comprises providing ground glass, and adding mill additions to the ground glass to form a mixture.
• the mill additions comprise silica and a zirconia compound and the mixture comprises at least about 15 parts and less than about 60 parts by weight of the silica mill addition per hundred parts by weight of the ground glass.
• the method further comprises applying the mixture to a metal substrate to form a coated substrate, and firing the coated substrate at a temperature of about 1000 to 1700° F. (538-927° C.) to form the water-resistant porcelain enamel coating.
• the invention provides a method of manufacturing a water-resistant porcelain enamel coating.
• the method comprises providing ground glass and adding mill additions to the ground glass to form a mixture.
• the mill additions comprise a zirconia compound including particles having a median particle size of less than about 10 microns.
• the mixture is applied to a metal substrate to form a coated substrate and the coated substrate is fired to form the water-resistant porcelain enamel coating.
• the substrate may a water heater.
• the invention provides a method of manufacturing a water-resistant porcelain enamel coating.
• the method comprises providing ground glass, and adding mill additions to the ground glass to form a mixture.
• the mill additions comprise a zirconia compound.
• the method further comprises applying the mixture to a metal substrate to form a coated substrate, and firing the coated substrate to form the water-resistant porcelain enamel coating.
• the zirconia compound mill additions may comprise at least about 10 and less than about 120 parts by weight per hundred parts by weight ground glass.
• the substrate may be a water heater.
• the process generally includes blending inorganic minerals and smelting the blend to form a red hot molten mixture.
• the molten mixture is poured from the smelter and quenched, for example, between water cooled rollers.
• the ribbon of glass may then be shattered to form glass frit.
• the resulting frit (or glass) may then be ground, for example, in a ball mill to reduce the frit to a predetermined particle size for the desired application.
• the grinding may be carried out wet or dry; typically, the grinding is carried out using water as the suspending medium.
• mill additions may be added to the ground frit.
• Typical mill additions include suspending agents, electrolytes, refractories, colors and opacifiers, and/or bisque strengtheners.
• the resulting mixture may then be applied to a substrate by any one of various application methods customary in the art, such as, brushing, dipping, spraying, etc.
• the coated substrate is then fired in a conventional furnace at a temperature at which the glass frit softens, but below the melting point of the metal substrate. Upon cooling, the vitreous enamel layer hardens to adhere to the substrate.
• the porcelain enamel coating of the invention may be prepared by providing ground glass; adding to the ground glass mill additions including a zirconia compound and silica (SiO 2 ) to form a mixture, applying the mixture to a metal substrate, and firing to form a porcelain enamel coating.
• a balance must be achieved between reducing the size and quantity of undesirable voids in the coating which facilitate corrosion, and maintaining sufficient bubble structure to avoid cracking or crazing. Hydrogen gas tends to escape from coated steel substrates which can cause cracking and crazing in coatings with insufficient bubble structure. This balance may be achieved with mill additions including an appropriate combination of a) silica and b) a zirconia compound.
• silica or zirconia compound mill additions are not significant.
• silica (SiO 2 ) and silicon carbide (SiC) may be suitable; silica is preferred.
• the silica mill addition is preferably present in an amount of greater than approximately 15 parts per hundred parts frit; more preferably greater than about 25 parts per hundred parts frit. All parts are given by weight unless otherwise indicated.
• the silica mill addition is preferably present in an amount less than about 60 parts per hundred parts frit; more preferably less than about 50 parts per hundred parts frit.
• the mill additions of a zirconia compound are preferably added in an amount of greater than approximately 10 parts per hundred parts frit based on the total weight of the mixture.
• the zirconia compounds are preferably added in an amount less than about 40 parts per hundred parts frit; more preferably less than about 30 parts per hundred parts frit.
• the combined total parts of the silica and zirconia compound mill additions is preferably less than about 70; the combined total parts is preferably greater than about 25 parts per hundred parts frit, more preferably greater than about 35 parts per hundred parts frit.
• zircon ZrO 2 .SiO 2
• zirconia ZrO 2
• ZrO 2 zirconia
• Employing finer particle sizes of the zirconia compound may permit an increase in the quantity of zirconia compound which may be employed. This, in turn, may increase the water resistance of the coating. Particle sizes of 200 mesh or finer are preferred.
• mill additions may also be included, such as clay, magnesium carbonate, sodium nitrite, borax, boric acid, potassium phosphate, potassium silica fluoride, or other mill additions customary for a particular application.
• Such mill additions are typically added in an amount of approximately 1 to 32 parts per 100 parts frit and are generally added to improve the workability of the coating before firing.
• Clay in an amount of about 5 weight percent (based on the total weight of the mixture) is preferred.
• the glass frit may be any of the well-known compositions used for making vitreous porcelain enamel. However, it has been found preferable to use a borosilicate glass frit and particularly an alkaline earth borosilicate frit, such as a sodium borosilicate glass.
• the glass is preferably lead-free.
• the composition of the glass frit may be modified to have lower water solubility by decreasing the fluorine and calcium contents, and by increasing the lithium content.
• a glass system comprising primarily silica (SiO 2 ), Na 2 O and zirconia (ZrO 2 ) with several additional oxides, may be modified to decrease the F 2 content, decrease the CaO content and increase the Li 2 O content.
• a desirable ground glass system comprises about 52 weight percent SiO 2 , about 17 weight percent Na 2 O, about 10 weight percent ZrO 2 , less than about 4.1 weight percent F 2 , less than about 0.005 weight percent CaO, and greater than about 4.1 weight percent Li 2 O.
• the mixture of frit and mill additions is applied to a substrate.
• the substrate is a metal and is preferably a steel. Most preferably, the substrate is a water heater.
• a preferred class of deposition techniques includes wet deposition techniques wherein the components of the coating are put into a liquid suspension, or “slip”, and then applied to the substrate using various wet application methods. For enamels being applied by a wet process, water is preferably used as the suspension medium.
• the coating thickness should be thin enough to permit gas to escape from the substrate. Thicknesses of about 9 to about 11 mils are typical.
• the firing temperature is preferably at least about 1000° F. (538° C.); more preferably at least about 1400° F. (760° C.) and most preferably at least about 1550° F. (843° C.).
• the firing temperature is preferably less than about 1700° F. (927° C.); more preferably less than about 1650° F. (899° C.).
• zirconia compounds using finer zircon (ZrO 2 .SiO 2 ) and zirconia (ZrO 2 ) has been found to improve the water resistance of the resulting coating. More particularly, zirconia compounds having median particle sizes of less than 100 microns have been found to show significant improvement in terms of water resistance.
• the term “fine zirconia compound” is meant to refer to at least one of zircon (ZrO 2 .SiO 2 ), zirconia (ZrO 2 ) or a combination thereof, having a median particle size of less than 10 microns.
• Preferred median particle sizes of fine zirconia compound may be about 0.1 to 10 microns, while about 0.1 to 5 microns is more preferred, and about 0.3 to 4 microns is most highly preferred.
• Spectrolux® manufactured by Continental Minerals in Cincinnati, Ohio. Spectrolux® is manufactured in four different grades, each of which is determined by median particle size: 1) very fine (0.3 to 4 microns); 2) fine (0.3 to 10 microns); 3) coarse (0.1 to 20 microns); and coarser (greater than 20 microns, but less than 100 microns). The fine and very fine grades of Spectrolux® are preferred.
• the amount of the fine zirconia compound used in the coating may depend on whether a hard, medium or soft frit is being used.
• hard frits include, but are not limited to, VS710 manufactured by A. O. Smith.
• medium frits include, but are not limited to, VS713 manufactured by A. O. Smith.
• soft frits include, but are not limited to, VS756 manufactured by A. O. Smith.
• Other examples of soft, medium and hard frits include those frits having similar physical and chemical properties as the examples set forth above. Unless otherwise specified, the ranges and ratios are provided below on the basis of parts by weight.
• fine zirconia compound per about 100 parts by weight ground glass When a hard frit is being used, about 0.001 to about 60 parts by weight fine zirconia compound per about 100 parts by weight ground glass may be used.
• the term “about” is being used herein to modify the numerical ratios, and reasonably extend the ranges and ratios listed above and below to cover ratios which still result in a water-resistant coating.
• at least about 10 parts by weight fine zirconia compound per 100 parts by weight ground glass will be used, although less than this amount may be employed.
• greater than about 10 and less than about 60 parts by weight fine zirconia compound per 100 parts by weight ground glass may be used.
• silica is employed without a zirconia compound, up to about 80 parts silica by weight per about 100 parts by weight ground glass may be used.
• greater than about 30 parts and less than about 70 parts silica by weight per about 100 parts by weight ground glass will be used in conjunction with a hard frit.
• a fine zirconia compound and a silica up to about 100 parts zirconia compound/silica by weight may be added per about 100 parts by weight ground glass.
• greater than about 20 parts and less than about 70 parts fine zirconia compound/silica by weight are added per about 100 parts by weight ground glass.
• a medium frit When a medium frit is being used, about 0.001 to about 90 parts fine zirconia compound per about 100 parts by weight ground glass may be used. Generally, at least about 30 parts fine zirconia compound per 100 parts by weight ground glass will be used. It is possible to use less than this amount, however. Preferably, greater than about 35 to less than about 75 parts by weight of fine zirconia compound per 100 parts by weight ground glass may be used. In comparison, when silica is employed without a zirconia compound, up to about 40 parts silica by weight per about 100 parts by weight ground glass may be used. Preferably, greater than about 35 parts and less than about 75 parts silica by weight per about 100 parts by weight ground glass will be used in conjunction with a medium frit.
• zirconia compound/silica by weight When adding a fine zirconia compound and a silica, up to 110 parts zirconia compound/silica by weight may be added per about 100 parts by weight ground glass. Generally, greater than 50 parts zirconia compound/silica by weight are added per about 100 parts by weight ground glass. Preferably, greater than about 25 and less than about 75 parts zirconia compound/silica by weight are added per about 100 parts by weight ground glass.
• the amount of fine zirconia compound per frit can be greatly increased. More specifically, about 0.001 to about 120 parts by weight fine zirconia compound per about 100 parts by weight ground glass may be used. Generally, at least about 30 parts by weight fine zirconia compound per 100 parts by weight ground glass are used, although less zirconia compound may be employed. Preferably, greater than about 30 to less than about 80 parts fine zirconia compound by weight per 100 parts by weight ground glass may be used. In comparison, when silica is employed without a zirconia compound, up to about 100 parts by weight silica may be used per about 100 parts of soft frit.
• greater than about 40 parts and less than about 80 parts silica by weight per about 100 parts by weight ground glass will be used in conjunction with a soft frit.
• a fine zirconia compound and a silica up to about 120 parts zirconia compound/silica by weight may be added per about 100 parts by weight ground glass.
• greater than about 30 parts zirconia compound/silica by weight are added per about 100 parts by weight ground glass, although less may be used.
• greater than about 30 and less than about 80 parts zirconia compound/silica by weight are added per about 100 parts by weight ground glass.
• anywhere from about 0.001 to about 120 parts by weight of zirconia per about 100 parts of ground glass may be added to ground glass, regardless of the frit being used.
• more zirconia compound may be added to ground glass when a fine zirconia compound is used, regardless of the frit. Consequently, the invention should in no way be limited to the type of frit being used.
• the more zirconia used in the frit the more water resistant the resulting mixture or coating becomes.
• the previously specified ranges will provide coatings having the best water resistance.
• fine zirconia may be used in Examples 1 and 2 set forth below. It should be noted that the higher the level of silica and zirconia compound added to the glass, the higher the temperature at which the coating will need to be fired. Generally firing will occur for about 4 to 10 minutes.
• a borosilicate glass frit is prepared having the following oxide content by weight.
• the frit is ground, and to 1000 parts of frit are added the following mill additions. Parts are given by weight. Weight percent is based on the total weight of the dry mixture of frit and mill additions.
• a slip is prepared by mixing the above ingredients with 25-30 weight percent water (based on the total weight of the slip solution). The slip is sprayed onto a steel substrate to a thickness from 30-60 grams dry per square foot of substrate. The sample is then fired to reach temperatures above 1500° F. (816° C.) for about 4 minutes with a maximum temperature of 1650° F. (899° C.). Water resistance of the resulting sample was tested by immersing the sample in a bath of 2% tetrasodium pyrophosphate at 205° F. (96° C.) for 56 days. The area of the porcelain enamel exposed was 5.4 square inches. The 20Zr/40Si coating had a weight loss of 0.09 grams. By comparison, the same area of commercial glass having silica mill additions and no zircon mill additions had a weight loss of 0.28 grams when subjected to the same test conditions.
• a porcelain enamel coating is prepared as described in Example 1 above except the zirconia compound and silica content from the mill additions is as indicated on Table 1 below.
• Table 1 shows the results of employing various quantities of silica (SiO 2 ) (represented as Si in Table 1) and zircon (ZrO 2 .SiO 2 ) (represented as Zr in Table 1).
• the quantities are in parts by weight per 100 parts glass frit.
• Water resistance is determined by immersing the coated part in a bath of 2% tetrasodium pyrophosphate at 205° F. (96° C.) for 11 days and then measuring weight loss (in grams). A smaller weight loss is preferred. The area of the porcelain enamel exposed for all samples was 5.4 square inches. By comparison, a commercially available water heater glass (having no zircon mill additions) tested under the same conditions was found to have a weight loss of 0.0238 grams; over two times greater weight loss than the improved coating of the present invention.
• a mill addition containing silica and no zirconia compound leads to poor adhesion and relatively large bubbles.
• using mill additions with a zirconia compound and no silica compound tends to result in poor fish scale resistance.
• Table 1 shows that zircon suppresses bubble or void formation.
• the compositions having a greater zircon content as a mill addition desirably exhibited a smaller percentage of bubble content and a smaller average bubble size.
• silica when silica is used in combination with zirconia as a mill addition, the relative water resistance of the resulting porcelain enamel is greater than the water resistance of a porcelain enamel made using mill additions of either silica alone or zircon alone. This synergy is most noticeable when silica is present in an amount of 15-45 parts per hundred parts frit while zirconia is present in an amount of approximately 10-30 parts per hundred parts frit.
• compositions of a number of examples employing a fine zirconia compound, silica or a combination thereof The numerical values indicate the weight in grams of each component of the compositions.
• the Examples vary in terms of the type of frit (namely, soft, medium or hard frit) being used.
• the fine zirconia compound in the Examples being utilized comprises Spectrolux® 6000.
• the median particle size of the fine zirconia compound in the Examples was about 1.278 microns.
• the silica in the Examples may comprise Aerosil, which is a fine silica commercially available from Degussa Chemical, Ridgefield Park, N.J., 325 mesh silica commercially available from Short Mountain Silica, Mooresburg, Tenn., or a combination thereof.
• the other components in the compositions may include PCD #1 Clay commercially available from Kentucky Tennessee Clay Company, Mooresburg, Tenn., PCD #3 Clay commercially available from Old Hickory Clay Company, Hickory, Ky., magnesium carbonate commercially available from Van Waters and Rogers, Cincinnati, Ohio, 10 M Borax obtained commercially available from Van Waters and Rogers, Cincinnati, Ohio, Bentonite commercially available from Van Waters and Rogers, Cincinnati, Ohio, and Bentone EW® commercially available from Rheox, Highttown, JN.
• the coatings were each fired for about seven minutes at the temperatures specified below. If not specifically listed in the Examples, the temperature at which the firing took place fell within the range the range of about 1500-1650° F. The preferred firing range is 1550 to 1600° F.
• VS756 soft frit
• VS713 medium frit
• VS710 hard frit
• 325 mesh silica 1000.00 PCD #1 Clay PCD #3 Clay Magnesium Carbonate 1.33 10 Mol Borox 5.33 Bentonite 1.33 Bentone EW 0.33 Aerosil (fine silica) 53.33 Zinc sulfide 4.00 Spectrolux ® 6000 200.00 WATER 567.0
• VS756 soft frit
• VS713 medium frit
• VS710 hard frit
• 325 mesh silica 1000.00 PCD #1 Clay PCD #3 Clay 62.50
• VS756 soft frit
• VS713 medium frit
• VS710 hard frit
• 1000 325 mesh silica
• Bentone EW 0.25 Aerosil fine silica
• Zinc sulfide 3.00 Spectrolux ® 6000 600.00 WATER 567.0
• VS756 soft frit
• VS713 medium frit
• VS710 hard frit
• PCD #1 Clay 12.5
• PCD #3 Clay 62.5
• Magnesium Carbonate 1 10 Mol Borox 4.00
• Bentonite 1.00
• Bentone EW 0.25 Aerosil fine silica
• Zinc sulfide 3.00 Spectrolux ® 6000 200.00 WATER 567.0
• VS756 soft frit
• VS713 medium frit
• VS710 hard frit
• Bentonite 1.00
• Bentone EW 0.25 Aerosil fine silica
• Zinc sulfide 3.00
• Spectrolux ® 6000 400.00 WATER 567.00
• the first column entitled “Initial Weight Grams” shows the initial weight in grams of each coating after firing.
• Each of the coatings in Examples 8-15 was introduced into water in order to measure the water resistance of each coating.
• the next column, “INSPECT 1,” shows the weight of the coating upon being inspected after it had been exposed to water for twenty-two days.
• the column, “INSPECT 2,” shows the weight of the coating after being inspected a day later.
• the coating loses weight as some of the material therein is dissolved into the water.
• the material loss in grams of each coating is shown in the column entitled the same.
• the total loss in weight of each coating is also listed below. The lower the total weight loss, the better water resistance the coating exhibits. In other words, less weight loss means the coating was less susceptible to the water to which it was exposed.
• all of the coatings including the fine zirconia exhibit better water resistance than standard glass having 35 percent silica mill additions with no zircon.

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Citations (27)

• 2002
  • 2002-07-08 US US10/190,957 patent/US7410672B2/en not_active Expired - Fee Related
• 2003
  • 2003-07-07 CA CA2492744A patent/CA2492744C/en not_active Expired - Lifetime
  • 2003-07-07 CN CNB038212765A patent/CN100509673C/zh not_active Expired - Lifetime
  • 2003-07-07 WO PCT/US2003/021066 patent/WO2004005209A1/en not_active Application Discontinuation
  • 2003-07-07 MX MXPA05000498A patent/MXPA05000498A/es active IP Right Grant
  • 2003-07-07 AU AU2003249705A patent/AU2003249705A1/en not_active Abandoned

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